Process for distilling pressure tar



Oct. v19, 1937. o. BEHIMER y PROCESS FOR DISTILLING PRESSURE TAR Filed Feb. 10, 1928 N dba.

Patented @et 19, 1937,-

, 2,095,963 PnocEss Fon ms'rmuNG massima 'rAn om nehmer, chicago, n1., assignor to The Texas Company, New York, N. Y., a corporation o of Delaware Application February 1o, is'zs, serial No. 253,259

, 3 Claims. The invention relates primarily to the recovery of lower boiling loils from the heavy residues which are withdrawn from the bottoms of stills. More particularly, the invention has reference to the distillation of suchtarry residues by means of theV self-contained heat in the latter at the time of its withdrawal from the still. Heretofore, it has been a common practice to re-run the residual material through suitable pressure tube stills which have been fired from rsome external source to drive off the vapors of lower boiling oils includedin the residue. More recently in the operation of pressure stills for'converting higher boiling oils to lower boiling constituents, the practice has developed of withdrawing the tarry bottoms'or residues from the stills under operation and introducing them into an expansion chamber or secondary still wherein the pressure is considerably below that in the main still. The pressure inthe expansion chamber may be maintained at substantially atmospherie and it will be apparent that under this condition much of the vapors which have been held in liquidl form in the main still due to the excessive pressure, will be released. However,

even this treatment of the residue has not beeng found to sufiiciently strip the tar of the' constituents of gasoline and lower boiling oils which may be useful as further cracking stock. For this reason it has been proposed in the past to subject the residue remaining in the expansion chamber to further treatment by means of steam injected into it in another drum. Thus, while no external heat has been applied in the expansion chamber, recourse .has been had to the heat content of the steam introduced into `the second.

chamber or drum to aid in the recovery of the valuable lighter components. v In accordance with the present invention, recovery of a maximum amount of the desirable lighter oils from the tarry residue is contemplated so that these constituents may be treated to form commercial gasoline or may be re-cycled through the pressure still. Toward this end the present invention contemplates the release of pressure upon the tar in several successive stages, the final stage being maintained under a vacuum or subatmospheric pressure, 1

Withthe foregoing and other incidental objects and vadvantages in view, the invention consists in the novel form vand arrangement of apparatus, one embodiment of which will new be explained in detail in connection with the accompanying drawing, in which the single figure illustrates diagrammatically a cracking system provided with the novel tar distillation apparatus.

For purposes of illustration, the invention has been disclosed with relation to cracking apparatus of the coil and Vdrunri type, in which the Vcharge of oil is first circulated through a preheating coil I0 by means of a pump II and then introduced into a large vertical c lrum I2. Coil I0 will be heated in any suitable way from an outside source and the drum I2 may be similarly externally heated or it may be merely insulated and operate byvirtue of the contained heat of the oil. The details of the construction of this portion of the apparatus are not material to the features of the present invention, it being understood that a variety of other cracking systems might be substituted for that shown. Ii' desired, a battery of stills or drums I2 might be provided, either with or without the preliminary preheating coil I0. Prior to introduction into the coil I0, furthermore, the oil may be heated by passage through an conomizer or any other heat exchange apparatus tending to utilize the heat 'of ,the ue gases or of the vapors 0r oil passing out of the system. Pressure vmaterially above atmospheric will ordinarily be maintained in the coil Ill and the' drum I2 and this pressure may either be uniform for both of these units or it may be greater in the coil. The vapors generated in the drum will be carried over by means Vof the pipe extending from the top of the latter to a bubble tower or other suitable condenser or dephlegmator I3. Those vapors which remain as such'throughout their passage through the tower i3 may be carried by vapor line I4 to a coil I5 of a iinal condenser. The latter will preferably be cooled by water and the condensate may be collected in an accumulator I6, having suitable provisions for leading oli the fixed gases.

` In the vapor line I4 there may, if desired, be located one or more reiiuxing condensers. From the bottom of the tower I3a line Il. having a pump therein is designed for the withdrawal of the condensate which accumulates in the tower and for the return of the latter to any suitable point of the coil I0.

Either periodically or continuously, residual oil or tarry material will be withdrawn from the bottom of the still I2 through a. line I8. While this withdrawal may be made continuous, it' is preferably done intermittently as the heavier 4tower 28 with the pump 25.

The pressure within the chamber 20 will preferably be atmospheric or as little above as may be required to force the generated vapors through the remaining apparatus. It will be apparent that upon the release of pressure upon the tarry residue within the chamber 20, vapors of the lower boiling oils which have been held in liquid form in the main still l2 by virtue of the high pressure will be given oit' and carried out of the top of the chamber into a, tower or dephlegmator 2l. Those vapors which remain as such within the dephlegmator are then passed through a iinal condenser 22 and into an accumulator 23. The product thus accumulated may be a relatively good grade of gasoline which may be discharged into a suitable storage tank and may, if desired, be mixed with the product from the accumulator I 6. From the bottom of the tower 2l the condensate may be withdrawn into a line 24 provided with a pump 25 by means of which the condensate formed from the heavier vapors may be re-cycled for further cracking along with the fresh charge. y

The portion of the residual tarry mass which remains in the chamber 20 is then withdrawn from thevbottom of the latter through a line provided with an expansion valve 26. This line serves to introduce the remaining material into a second chamber 21 which is maintained under a vacuum or subatmospheric pressure. Discharge of the residue into the chamber 21 will preferably take place at intermittent periods, although continuous discharge may be effected if so desired. It will be apparent that vapors which were held back at the atmospheric or slightly higher pressure in the chamber 20 will be released within the chamber 21 and may be carried oif through a vapor line at the top into a tower or similar dephlegmator 28, from which the vapors pass into a nal condenser 29 and an `accumulator 30. The condensate so formed may be inthe nature of gasoline, having substantially the same qualities as that collected in the drums I6 and 23, or it may be of somewhat higher endpoint, as desired. 'I'he vacuum within the chamber 21 may be maintained in any suitable way as by the provision of a vacuum pump 3l beyond might be located between the chamber 21 and the dephlegmator 28 or between the latter and the final condenser, or between the condenser and the accumulator 30, so long as the desired subatmospheric pressure is maintained within the chamber 21. 'I'he condensate which collects in the base of the tower 28 will preferably be recycled through the system for further cracking, just as in the case of the condensate collected within the rst tower 2|. For this purpose a. line 33 may serve to connect the bottom of the Suitable valves should be provided in the lines 2l and 33 to enable the pump 25 to be connected to either the tower 2lor tower 28 or both. That portion of the residue whichstill remains in tarry form'F within the chamber 21 may be withdrawn and discharged into a storage tank 34. Further'treatment o! thismaterialmay be employed if deaired', although after distillation by virtue of the recovered. Normally, no other heat will be required to be applied to the chambers 20 and 21 from any external source, although the opera- .tion of distillation may be aided by the use of steam in one or both of the chambers, if desired.

While the invention has been disclosed in connection with a system involving only a single still, it will be understood that a battery of stills, or even a number of batteries, may discharge into the same series of expansion chambers 20 and 21, if desired. Furthermore, the number of expansion chambers connected in series to form successive stages of expansion need not be limited to the two illustrated but may comprise a greater plurality, if desired.

It will be apparent that numerous changes the apparatus which has been described and that the specic description has been given merely for the purposes of illustrating one suitable form of the invention. It is desired to be limited only by the scope of the claims which follow.

What I claim is:

1. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process l, may be made in the form and arrangement of l that comprises subjecting the oil to cracking temperature under superatmospheric pressure to eiect cracking in a cracking still wherein separation of vapors from liquid takes place, withdrawing the separated liquid from the cracking still and expanding it into an unheated stripping still maintained under a reduced pressure approximating atmospheric to effect vaporization of gasoline constituents and higher boiling point or intermediate constituents, passing the resultant vapors into a fractionating tower and subjecting them to fractionation therein to separate out the gasoline as an overhead vapor frac` tion and a reux condensate comprising said intermediate constituents, condensing said vapor fraction to form a gasoline distillate, passing the unvaporized residue from said stripping still to a second stripping still, maintaining the second stripping still under a vacuum to eiect further vaporization to separate out as vapors heavier constituents without the aid of Yadded heat, recovering a condensate from said vapors adapted as charging stock to a cracking zone and with drawing the resultant stripped residue from said second stripping still to remove it from the system.

2. In the conversion of higher boiling hydrolcarbon oils into lower boiling ones, the process ,that comprises subjecting the oil to cracking temperature under superatmospheric pressure to effect cracking in a cracking zone, withdrawing liquid from the 'cracking zoneand expanding it into an unheated stripping still maintained under a/reduced pressure approximating atmospheric to eect vaporization of gasoline constituents and higher boiling point or intermediate constituents, passing the unvaporized residue from said stripping still to a second stripping still, maintaining the second stripping still under a vacuum to effect further vaporization to separate out as vapors heavier constituents without the aid of added heat, recovering a condensate from said vapors adapted as charging stock tev a cracking zone and withdrawing the resultantstripped residue from said second stripping still to remove it from the system.

3. That improvement in methods of extracting oils of intermediate boiling point from a complex hydrocarbon mixture containing the same, which comprises subjecting a heated and continuously owing stream oi' the mixture to the following steps in the sequence named: First, removing at substantially atmospheric pressure the low boiling `point `oils contained in the continuously ilowing mixture; second, withdrawing through a pressure reducing and regulating valve the continuously flowing mixture from which the lower boiling point oils have been extracted; third, placing under a single high vacuum the 

